<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<button id="box">aaaa</button>
<script>
    var b = document.getElementById('box');
    console.log(b);


    /*
    *自定义对象
    *
    *浏览器提供的对象 document. window
    *
    * 内置对象 Math.round(),Math.random()
    *
    * */
</script>
</body>
</html>